In Java how can I validate a thrown exception with JUnit?

Question

When writing unit tests for a Java API there may be circumstances where you want to perform more detailed validation of an exception. I.e. more than is offered by the @test annotation offered by JUnit.

For example, consider an class that should catch an exception from some other Interface, wrap that exception and throw the wrapped exception. You may want to verify:

1. The exact method call that throws the wrapped exception.
2. That the wrapper exception has the original exception as its cause.
3. The message of the wrapper exception.

The main point here is that you want to be perf additional validation of an exception in a unit test (not a debate about whether you should verify things like the exception message).

What's a good approach for this?

Answer 1

As provided in your answer, it's a good approach. In addition to this:

You could wrap the function expectException into a new Annotation, called ExpectedException.
An annotated method would look like this:

@Test
@ExpectedException(class=WrapperException.class, message="Exception Message", causeException)
public void testAnExceptionWrappingFunction() {
  //whatever you test
}

This way would be more readable, but it's exactly the same approach.

Another reason is: I like Annotations :)